Facile Synthesis of Fe3O4@Tannic Acid@Au Nanocomposites as a Catalyst for 4-Nitrophenol and Methylene Blue Removal

A facile, cost-effective, and eco-friendly method was proposed to synthesize Fe3O4@tannic acid@Au nanocomposites (Fe3O4@TA@Au). First, Fe3O4 nanoparticles with diameters of 20 and 200 nm were synthesized by co-precipitation and solvothermal methods, respectively. Gold nanoparticles were deposited on magnetic Fe3O4 through tannic acid-metal-polymer intermediate-layer-mediated reductions. The catalytic activities of the as-prepared Fe3O4@TA@Au were investigated by spectroscopically monitoring the reduction of 4-nitrophenol (4-NP) and methylene blue (MB), which could be achieved within several minutes with an excess of NaBH4. The impact of the Fe3O4 size on the overall catalytic ability of the Fe3O4@TA@Au was systematically studied. The reaction rate constants of the Fe3O4-20 nm@TA@Au for 4-NP and MB reduction were 0.432 and 0.543 min–1, respectively. For the Fe3O4-200 nm@TA@Au nanocomposite, the optimized reaction rate constants for 4-NP and MB reduction were 3.09 and 0.441 min–1, respectively. Due to magnetic separation, the Fe3O4@TA@Au could be easily harvested and recycled. After five recycling cycles, the catalytic ability remained over 90%, and the recycling process could be completed in several minutes, highlighting its potential as a catalyst for 4-NP and MB removal.